A conventional hand-operated air pump can be categorized into direct pumping type and air storage type. An air pump of direct pumping type operates by manually pumping air into an air chamber of the air pump, and the air flows into a to-be-inflated object via an air tube unit of the air pump. The air delivered into the object has a relatively low pressure, and thus this type of air pump is suitable for inflating balloons, low pressure tires, etc. On the contrary, an air pump of air storage type is configured with an air storage cylinder that stores high pressure gas, which can be delivered to an object to inflate the object. Since the two types of air pumps have different ways of air delivery and have different structures, a user has to purchase both types of the air pumps in order to fulfill needs of inflating objects that require high pressure gas and inflating objects that require low pressure gas.
The applicant of this disclosure designed a conventional air pump device which is disclosed in Taiwanese Patent No. 1495788 and which is capable of outputting low pressure gas and high pressure gas. The conventional air pump device is configured with an air generating mechanism and an air cylinder that are fixedly coupled to each other. However, the air generating mechanism and the air cylinder cannot be separated and cannot be individually operated.